Pyrometric Temperature Measurements Research Articles

Influence of geometry variations during pyrometric temperature measurement in laser material processing

Pyrometric temperature measurements, essential for quality assurance in laser processing, are challenged by the angular dependence of emissivity with varying local geometries. Therefore, this contribution presents investigations on the influence of geometry variations on pyrometric temperature measurements for geometry variations at different measurement positions and within the measurement spot.For this, laser-heated copper samples with chamfers are used and the measurement spot of the pyrometer is moved over the edge of the chamfer to cover different geometric areas. Three chamfer angles and three measurement spot sizes were examined. In addition, a theoretical calculation has been performed and compared with the experimental results. The study shows the significant influence of geometry variations on the pyrometric temperature measurement.

The role of self-fluidization in combustion synthesis of porous and granular Ni-Al intermetallics

A wide range of capillary processes participates in the structural transformation of the reacting metal powders during the combustion synthesis of intermetallics. Using additives that decompose in the combustion wave allows controlling the formation and interaction of melts that open new opportunities for direct manufacturing of materials with desired shape and structure, which are ready for applications without additional processing steps. This paper studies the combustion mechanism of Ni+Al powder mixtures (average size of particles 10 µm) doped with CaCO3. The methods of high-speed imaging, pyrometric temperature measurements, and reaction quenching were used. It was found that CaCO3 decomposes in the preheat zone of the combustion wave resulting in the fluidization of the powder mixture. In the reaction zone of the combustion wave, an ensemble of moving microdroplets with a diameter of 0.1–0.2 mm forms. Some microdroplets drift in a preheat zone of the combustion wave, which stimulates the fluidization process. The microdroplets ultimately form larger droplets with a diameter of up to 2 mm that crystallize and form spherical struts of the gas-permeable scaffold of the combustion products. Synthesis of intermetallic compounds couples with the formation of calcium aluminates, which affects the processes of reaction coalescence and the structure of combustion products. For the CaCO3 concentration below 5–8%, the combustion products represent strong porous scaffolds consisting of tightly fused spherical-like intermetallic struts forming a net of mm-sized interconnected pore channels. Brittle scaffolds comprised of detached intermetallic granules with a diameter of 25–200 µm separated by oxide layers form if CaCO3 concentration exceeds 14%. The washing-out of the oxide phases with 5% hydrochloric acid allows for obtaining the powder of the remaining granules. The effect of self-fluidization on the structure of the synthesized alloys has been discussed in detail.

Measurements of the melting points, liquidus, and solidus of the Mo, Ta, and Mo[sbnd]Ta binary alloys using a novel high-speed pyrometric technique

The measurement of high phase-transition temperature is equally challenging and useful for developing high-temperature materials for critical applications. Pyrometer is a suitable option to measure the phase-transition temperature above 2300 K. In this work, Mo, Ta, and their isomorphous binary alloys are selected as the target system for high-speed pyrometer temperature measurements in the arc-melting setup. The present phase transitions (melting point, solidus, and liquidus) measurements indicate that the MoTa is an isomorphous system with a narrow freezing range (i.e., an average value < 35 K). The results from this present work would change the existing MoTa phase diagram. The Gibbs energy modeling for liquid (L) and BCC_A2 (α) phases of the MoTa system are then performed, including the latest experimental results from this work. The applications of the current experimental methodology could be extended to measure the high phase-transition temperatures in superalloys with significant commercial values.

Simultaneous Raman and pyrometric temperature measurements in shock-wave-compressed toluene

We fielded experiments to compare temperatures measured simultaneously by pyrometry and Raman spectroscopy in toluene shocked to 9 GPa. A 0.5 mm thick toluene sample was compressed between sapphire windows by plate impact from a gas gun. As the shock wave reverberated between the windows, the pressure increased stepwise to about 9 GPa. While the sample was near its peak pressure, we measured the Raman spectrum and determined temperature from the ratio of the Stokes and anti-Stokes intensities. Simultaneously, we measured the sample thermal radiance from the C-H vibration bands that occur between 3.2 and 3.6 μm to determine temperature pyrometrically. The pyrometer used a biased indium antimonide detector paired with a custom transimpedance amplifier, a system capable of temperature measurements as low as about 400 K. The Raman measurements gave a temperature of 530 ± 25 K in the bulk volume of toluene. Pyrometry gave a temperature of 496 + 15/−20 K, which is in reasonable agreement with the Raman measurement. Comparisons of this type are necessary to validate pyrometry as a temperature diagnostic in dynamic experiments.

Reduction of uncertainty with non-contact measurement of temperature

The results of calculated theoretical and experimental studies aimed at justifying the use of calibrators, allowing to take into account the uncertainties associated with the difficulty of taking into account the radiation coefficients of controlled surfaces in non-contact pyrometric temperature measurements are given in the work. The relevance of the research is related to the requirements for ensuring the accuracy of non-contact temperature measurements at the level of instrumental errors of pyrometers declared by their manufacturers. Currently, pyrometric measurements are used in virtually all industries and this causes the relevance of the presented research results and proposed technical solutions. The functional scheme of the calibrator using replaceable surface samples is proposed, the temperature of which is measured by pyrometers.

Density of Liquid Tantalum and Estimation of Critical Point Data

In order to determine the density of tantalum over the entire liquid phase (at the pressure applied) and several hundred K into the super-heated region, the method of ohmic pulse-heating was applied. For this purpose, images of the thermal radial expansion of the resistively heated sample wires were taken with an adapted CCD system. A newly integrated high-power photoflash and improved triggering of the experiment allowed the acquisition of high-contrast shadow images of the expanding wires. To reduce the uncertainty arising from simultaneous pyrometric temperature measurement, the change in normal spectral emissivity as a function of temperature was additionally taken into account. In this work, the density versus temperature relationship of tantalum is reported and compared to existing literature data. From the newly obtained liquid-phase density, critical point data of tantalum, such as critical temperature and critical density, were estimated via an extrapolation procedure. Furthermore, an estimate of the phase diagram in the density versus temperature plane is given. The work is concluded by a rigorous density uncertainty estimation according to the guide to the expression of uncertainty in measurement (GUM).

Пирометр для измерения температуры расплавов

Пирометр для измерения температуры расплавов

Performance of photomultipliers in the context of laser-induced incandescence.

Photomultiplier tubes (PMTs) are widely used as detectors for laser-induced incandescence (LII), a diagnostics method for gas-borne particles that requires signal detection over a large dynamic range with nanosecond time resolution around the signal peak. Especially when more than one PMT is used (i.e., for pyrometric temperature measurements) even small deviations from the linear detector response can lead to significant errors. Reasons for non-linearity observed in other PMT measurement techniques are summarized and strategies to identify non-linear PMT operation in LII are outlined. To quantify the influence of the non-linear behavior, experiments at similar light levels as those encountered in LII measurements are carried out, and errors propagated in two-color pyrometry-derived temperatures are determined. As light sources, a calibrated broadband light source and light-emitting diodes (LEDs), centered at the bandpass filter wavelengths of the LII detectors, were used. The LEDs were operated in continuous and pulsed (<300 ns) mode, respectively, to simulate DC background radiation (e.g., from sooting flames) and similar pulsed signal traces as in typical LII measurements. A measured linearity deviation of up to 10% could bias the temperature determination by several hundred Kelvin. Guidelines are given for the design and the operation of LII setups, which allow users to identify and prevent errors.

Thermophysical Properties of Five Industrial Steels in the Solid and Liquid Phase

The need for characterization of thermophysical properties of steel was addressed in the FFG-Bridge Project 810999 in cooperation with our partner from industry, Böhler Edelstahl GmbH & Co KG. To optimize numerical simulations of production processes such as plastic deformation or remelting, additional and more accurate thermophysical property data were necessary for the group of steels under investigation. With the fast ohmic pulse heating circuit system and a commercial high-temperature Differential Scanning Calorimeter at Graz University of Technology, we were able to measure the temperature-dependent specific electrical resistivity and specific enthalpy for a set of five high alloyed steels: E105, M314, M315, P800, and V320 from room temperature up into the liquid phase. The mechanical properties of those steels make sample preparation an additional challenge. The described experimental approach typically uses electrically conducting wire-shaped specimen with a melting point high enough for the implemented pyrometric temperature measurement. The samples investigated here are too brittle to be drawn as wires and could only be cut into rectangular specimen by Electrical Discharge Machining. Even for those samples all electrical signals and the temperature signal can be recorded with proper alignment of the pyrometer. For each material under investigation, a set of data including chemical composition, solidus and liquidus temperature, enthalpy, electrical resistivity, and thermal diffusivity as a function of temperature will be reported.

Single wavelength and ratio pyrometry reflection errors in temperature measurement of gas turbine blade

Radiation thermometers are the instruments most opted for when measuring surface temperatures of high speed rotating parts non-intrusively in many industrial applications. However, reflection of ambient radiation from the measured target goes against the operating principles of most of these thermometers thus introducing errors to the temperature measurements. Reflection errors introduced into single wavelength and ratio pyrometer temperature measurements of a rotating cooled gas turbine blade were investigated in this work through simulation. Errors for the two pyrometers based on varied target surface emissivity, view factor and ambient temperature were calculated. At high ambient temperatures, high view factors and low surface emissivity, errors exceeding 70% and 30% were realized for single wavelength and ratio pyrometers respectively. Thus temperature measured on reflective targets surrounded by surfaces at much higher temperature should be corrected for reflection errors if its reliability is to be guaranteed.

Pyrometric temperature measurements with a miniature cavity used as a blackbody in the calorimetric method for determining absorbed laser energy

As a result of improvements introduced in the design parameters of detectors, the miniaturization of measuring gauge and software upgrades, today’s single band pyrometers are robust devices with innovative solutions developed to enhance their performance. Despite technological advances, entering the correct value of emissivity coefficient of an object in the pyrometric measuring system is still an unsolved problem. One of the possible solutions may be using a blackbody to a greater extent. This study attempts to use a miniature cavity as a blackbody in pyrometric temperature measurements of a metal part, conducted according to the so-called calorimetric (thermometric) method of determining the laser energy transferred to the part. The method helps measure the temperature of a laser-processed material that acts as a calorimeter. Temperatures are normally measured using thermocouples bonded to the laser-treated element, but this technique is not free from limitations. Some of them can be eliminated through pyrometric measurements. The experimental investigations involved simultaneous temperature measurements with the use of a thermocouple fixed to the processed element and a pyrometer for measuring the temperature of the miniature blackbody cavity produced in the material. Comparative study results support the use of a blackbody for calorimetric non-contact temperature measurements of laser energy absorbed in the welded part in laser beam welding.

Thermal Diffusivity and Thermal Conductivity of Five Different Steel Alloys in the Solid and Liquid Phases

The need for characterization of thermophysical properties of steel and nickel-based alloys was addressed in the FFG-Bridge Project 810999 in cooperation with a partner from industry, Bohler Edelstahl GmbH & Co KG. To optimize numerical simulations of production processes, such as remelting or plastic deformation, additional, and more accurate data were necessary for the alloys under investigation. With a fast ohmic pulse heating circuit system, the temperature-dependent specific electrical resistivity, density, and specific heat capacity for a set of five high alloyed steels were measured. Hence, using the Wiedemann–Franz law with a Lorenz number of $$L =2.45\times 10^{-8}\,\hbox {V}^{2}{\cdot }\hbox {K}^{-2}$$ , the thermal diffusivity and thermal conductivity could be calculated for the solid and liquid phases up to temperatures of 2500 K. This experimental approach is limited by the following requirements for the specimens: they have to be electrically conducting, the melting point has to be high enough for the implemented pyrometric temperature measurement, and one has to be able to draw wires of the material. The latter restriction is technologically challenging with some of the materials being very brittle. For all samples, electrical and temperature signals are recorded and a fast shadowgraph method is used to measure the volume expansion. For each material under investigation, a set of data including the chemical composition, the density at room temperature, solidus and liquidus temperatures, and the change of enthalpy, resistivity, density, thermal conductivity, and thermal diffusivity as a function of temperature is reported.

Pyrometric cathode temperature measurements in metal halide lamps

Time-averaged temperature distributions along the electrodes of vertically operated high-intensity discharge lamps with cylindrical quartz burners filled with mercury and additives of NaI, TlI and DyI3 have been measured. The lamps have been driven by 120 Hz switched-dc currents between 0.4 and 1.78 A and the measurements have been performed during the cathodic phase at the lower electrode. All considered currents are characterized by a diffuse arc attachment. For the correction of disturbing effects the measured distributions have been fitted with solutions of the quasi-one-dimensional and steady-state energy balance of a rod-shaped tungsten cathode. A model of the near-cathode layer in a multi-species plasma has been applied for the determination of the boundary layer characteristics where the work function has been treated as a free parameter. The required plasma component concentrations have been estimated from spectroscopic measurements in the arc column. The fit procedure includes the adjustment of the extension of the lateral arc attachment region which has a distinct impact on the determined tip temperature, power input from the plasma into the cathode and the work function. For the latter the tungsten value has been verified in the pure Hg lamp, but strong deviations result in the case of a TlI admixture. The lamp with DyI3 clearly shows the gas-phase emitter effect of lowering the work function induced by Dy.

Calibration of Temperature Measurement by Infrared Pyrometry in MicrowaveHeating of Powder Materials: an Exothermic Reaction Based Approach

Accurate temperature measurement remains a challenge for microwave heating of powder materials. We propose a temperature calibration method based on exothermic reactions and the resultant thermal runaway that occurs during microwave heating. The approach was demonstrated on microwave heating of four titanium alloys. Differential scanning calorimetry was used to determine the threshold reaction temperature for each selected titanium alloy. This served as a standard for the microwave heating of these titanium alloys. Infrared pyrometric temperature measurements were then calibrated by comparing the starting temperature of each thermal runaway event with the threshold reaction temperature.

Fastin situphase and stress analysis during laser surface treatment: A synchrotron x-ray diffraction approach

An in situ stress analysis by means of synchrotron x-ray diffraction was carried out during laser surface hardening of steel. A single exposure set-up that based on a special arrangement of two fast silicon strip line detectors was established, allowing for fast stress analysis according to the sin(2)ψ x-ray analysis method. For the in situ experiments a process chamber was designed and manufactured, which is described in detail. First measurements were carried out at the HZG undulator imaging beamline (IBL, beamline P05) at the synchrotron storage ring PETRA III, DESY, Hamburg (Germany). The laser processing was carried out using a 6 kW high power diode laser system. Two different laser optics were compared, a Gaussian optic with a focus spot of ø 3 mm and a homogenizing optic with a rectangular spot dimension of 8 × 8 mm(2). The laser processing was carried out using spot hardening at a heating-/cooling rate of 1000 K/s and was controlled via pyrometric temperature measurement using a control temperature of 1150 °C. The set-up being established during the measuring campaign allowed for this first realization data collection rates of 10Hz. The data evaluation procedure applied enables the separation of thermal from elastic strains and gains unprecedented insight into the laser hardening process.

Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps

The dependence of the gas phase emitter effect of Dy on a variation of the operating frequency between a few Hz and 2 kHz is investigated in a high intensity discharge lamp. The buffer gas of the lamp consisting of Ar, Kr and predominantly Hg is seeded with DyI3, its burner vessel is formed from transparent yttrium–alumina–garnet material. Phase and spatial resolved emission spectroscopy in front of the lamp electrode and pyrometric temperature measurements along the tungsten electrode are performed with a spectroscopic setup. Dy atom and ion densities in front of the electrode are deduced from absolute intensities of optically thin Dy lines and a plasma temperature, derived from the absolute intensity of mercury lines. Phase resolved values of the electrode tip temperature Ttip and input power Pin are obtained from temperature distributions along the electrode. Distinctly higher Dy ion and atom densities are measured in front of the electrode within the cathodic phase. With increasing operating frequency a reduction in both atoms and ions is observed in front of the cathode. In contrast, an increase in the ion density in front of the anode is seen. Moreover, the Dy ion density is drastically reduced by an additional seeding of the lamp with TlI. It is found that an up rating of the Dy ion density is correlated with a decline of Ttip and Pin. At higher frequencies this effect takes place not only within the cathodic phase but also within the anodic phase. The reduction of the average electrode tip temperature of the order of several hundred kelvin compared with a YAG lamp with a pure mercury filling is explained by a Dy monolayer on the electrode surface which is sustained by a Dy ion current.

Thermophysical properties of 22 pure metals in the solid and liquid state – The pulse-heating data collection

The workgroup of subsecond thermophysics in Graz has a long tradition in performing fast pulse- heating experiments on metals and alloys. Thereby, wire-shaped specimens are rapidly heated (10 8 K/s) by a large current-pulse (10 4 A). This method provides thermophysical properties like volume-expansion, enthalpy and electrical resistivity up to the end of the liquid phase. Today, no more experiments on pure metals are to be expected, because almost all elements, which are suitable for pulse-heating so far, have been investigated. The requirements for pulse-heating are: a melting point which is high enough to enable pyrometric temperature measurements and the availability of wire-shaped specimens. These elements are: Co, Cu, Au, Hf, In, Ir, Fe, Pb, Mo, Ni, Nb, Pd, Pt, Re, Rh, Ag, Ta, Ti, W, V, Zn, and Zr. Hence, it is the correct time to present the results in a collected form. We provide data for the above mentioned quantities together with basic information on each material. The uniqueness of this compilation is the high temperature range covered and the homogeneity of the measurement conditions (the same method, the same laboratory, etc.). The latter makes it a good starting point for comparative analyses (e.g. a comparison of all 22 enthalpy traces is in first approximation conform with the rule of Dulong-Petit which states heat capacity - the slope of enthalpy traces - as a function of the number of atoms). The data is useful for input parameters in numerical simulations and it is a major purpose of our ongoing research to provide data for simulations of casting processes for the metal working industry. This work demonstrates some examples of how a data compilation like this can be utilized. Additionally, the latest completive measurement results on Ag, Ni, Ti, and Zr are described.

Pyrometric temperature measurement of ceramic thermal shock samples

The determination of critical failure parameters during thermal shock requires a time and space resolved temperature measurement of the sample. High frequency pyrometry is a suitable technique for such a measurement task, which usually requires the knowledge of the optical properties of the investigated material. Another challenge is the infrared transparency of materials to be checked in the wavelength range of the pyrometer. The thermal shock disks are very thin, due to the need of homogeneous temperature distribution and to maintain a two-dimensional problem. To allow a pyrometric temperature measurement a universal calibration method for high frequency infrared cameras has been developed. Pyrometry in various media was demanded, as well as the estimation of optical properties (reflection, transmittance and emission) for the selected ceramics to be tested.

Testing a solar-blind pyrometer

Surface temperatures are key parameters in many concentrated solar radiation applications. Pyrometric temperature measurement of solar irradiated material surfaces is the alternative to contact measurement techniques, which are inadequate for measuring the temperatures of such surfaces. However, reflected solar radiation is an important uncertainty variable in this non-contact methodology. A promising method for eliminating this solar perturbation is by using centred passband filters on the atmospheric solar absorption bands, creating solar-blind pyrometric systems. A commercial pyrometer has been tested in the wavelength band at around 1.4 µm in the solar furnace at Plataforma Solar de Almería, showing its advantages and limitations. An estimation of temperature measurement uncertainty for a real case is presented with theory and experiment in agreement: the higher the temperature, the lower the uncertainty. Another experiment has shown that the pyrometer measures temperature properly even through quartz windows in this spectral range.

Temperature Calibration Techniques for TMF Testing

Abstract One of the methods to control the rapid temperature changes during a thermomechanical fatigue (TMF) test involves the use of an infrared pyrometer for temperature measurement. The infrared pyrometer relies on the emissivity of the test coupon. One way to determine this emissivity is to use a disappearing filament pyrometer. This paper presents two emissivity calibration techniques: Strain measurement and application of non-permanent thermocouples. Both techniques were applied for TMF testing, and the advantages and disadvantages of these techniques are described. The results show that the temperature indicated by these methods can significantly differ when compared to the actual temperature of the test specimen measured by thermocouples. However, these variances can be mitigated by calibration.